The Food and Drug Administration on Wednesday recommended that hospitals and doctors continue using forced air thermal systems during surgeries, despite thousands of lawsuits that allege 3M’s warming blankets increase the risk of serious surgical infections.

The Bair Hugger Forced Air Warming Device, manufactured by Maplewood-based 3M Co., is a widely used system that is supposed to promote post-surgical healing and cut down on infections by maintaining a patient’s body temperature in surgery.

More than 2,000 people have sued 3M, claiming the company has covered up evidence that the device actually increases infection risk by spreading contaminants with blown air and waste heat.

The concerns have apparently spooked some hospitals so much they have stopped using the system. The FDA said Wednesday the agency has concluded from all the available evidence that hospitals and patients should continue to use forced air systems in cases where it is “clinically warranted,” such as during joint replacement surgery. 

“The agency has no conclusive evidence to establish an association between use of a forced air thermal regulating systems and an increased risk of surgical-site infections,” FDA spokeswoman Stephanie Caccomo said via e-mail.

General anesthesia can compromise the body’s ability to regulate its temperature, especially during major surgeries in which internal tissues are exposed to the open air for long periods of time. This unintended hypothermia during surgery can increase infection rates, recovery times and mortality rates, according to studies cited by 3M on its Bair Hugger website. More than 80 percent of U.S. hospitals have a Bair Hugger unit, 3M said.

The Bair Hugger includes a device that sucks in air at room temperature and blows it out warm, plus a plastic “blanket” laid on the patient that fills up with the warm air like an inflatable swimming pool lounger.

Critics allege that the system may promote infections by moving contaminated particles around the patient, especially bacteria from the nonsterile floor of the operating room. The lawsuits say 3M knew about these risks and failed to fix them, and even tried to silence critics who could have exposed it.

More than 2,600 patient lawsuits from all 50 states have been consolidated into a single federal case in Minnesota, and Minnesota residents have also filed additional cases in state court. In the past two months judges in the state and federal cases have ruled evidence so far is not strong enough to grant requests to seek punitive damages against 3M.

“While it is undisputed that surgeries have been conducted using the Bair Hugger system for more than 25 years, plaintiffs present no evidence that any doctor has ever reported to 3M or (3M subsidiary) Arizant that the Bair Hugger system caused his or her patient to develop a surgical site infection,” Ramsey County District Judge William H. Leary III wrote Aug. 18 in an order denying permission to seek punitive damages.

Dr. Robert Quickel, vice president of surgery and procedural care for regional health system Allina Health, said every operating room in the 13-hospital system is equipped with the Bair Hugger unit. He estimated the devices are collectively used thousands of times a year. About a year and a half ago Allina officials reviewed evidence on forced-air systems and infection risks, and didn’t see the need to discourage the use of the Bair Hugger, he said.

Genevieve Zimmerman, an attorney with Meshbesher & Spence handling Bair Hugger litigation, said the FDA’s letter to doctors Wednesday was not surprising given that the agency cleared the 3M device for marketing. But she noted, “Often times the FDA reverses course in the face of new evidence, and often times it is the work of others outside the manufacturing industry that impact such a reversal of course. Plaintiffs stand by claims made in this litigation.”

The Bair Hugger’s original inventor, Dr. Scott Augustine, has said 3M was made aware of the problems with the device before buying its maker, Eden Prairie’s Arizant, in an $800 million acquisition in 2010. Augustine has said “there is no question” that waste heat created by the Bair Hugger spreads contaminants.

Although Wednesday’s FDA letter to doctors makes no specific reference to its product, 3M welcomed the communication. “Patient warming is supported by leading health care institutions and professional societies, including the FDA, and the Bair Hugger system has been proven to be a safe, effective and efficient method of doing so,” 3M spokeswoman Fanna Haile-Selassie said.